feature

4.5 to 20V Input Voltage Range Control Turn-On 0.4a, 0.8a and Adjustable Current Limit Options Under-Voltage Lockout Thermal Shutdown <10µA Shutdown Current Auto-Restart Fault Blanking RoHS Compliant

application

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General Instructions

The fpf2500 to fpf2506 are a series of load switches that provide comprehensive protection for systems and loads encountered in high current situations. These devices contain 0.23Ω current-limited n-channel MOSFETs that can operate over an input voltage range of 4.5-20V. The switch is controlled via a logic input (on) control signal capable of directly interfacing with the low voltage. Each part has thermal shutdown protection which closes the switch to prevent overheating in a sustained overcurrent condition. Operates in constant current mode when the switch current reaches the current limit to prevent excessive current that can cause damage. For fpf2500, fpf2501, FPF2503 and FPF2505, if the constant current condition still exists after 5 ms, these parts will turn off the switch, and for fpf2503 and fpf2505, the fault signal pin (flagb) will be pulled low too. The fpf2500, fpf2503 and fpf2505 have an auto-restart feature that will turn the switch on again after 640ms if the ON pin is still active. The FPF2501 does not have this auto-restart feature that keeps the switch closed until the open pin cycles. For the fpf2502, fpf2504 and fpf2506, a current limit condition will immediately pull the fault signal pin low and the part will remain in constant current mode until the switch current falls below the current limit. For FPF2500 through FPF2502, the minimum current limit can be from 500mA to 2A. For the FPF2503 and FPF2504, the minimum value is the current internally fixed at 400mA , while the current for the FPF2505 is internally fixed at 400mA and the fpf2506 is internally fixed at 800mA. These parts are available packaged in space saving 5-pin SOT33.

Instructions

The fpf2500-fpf2506 are current-limiting switches protecting systems and loads that may be damaged or interrupted by applying large currents. At the heart of each device is a 0.23Ω n-channel MOSFET and one capable of operating over a wide input operating range of 4.5 V-20 V. The controller has undervoltage lockout and thermal shutdown through current limit. The current of the fpf2500, fpf2501 and fpf2502 is limited by selection of external resistors. The minimum current of fpf2503 and fpf2504 is internally fixed at 400mA, while the current of FPF2505 is internally fixed at 400mA and fpf2506 is internally fixed at 800ma. On/Off Control The ON pin controls the state of the switch. When open high, the switch is on. Keeps active as long as there are no faults, the switch is on. For the owner version, an undervoltage or over 140 °C on the VIN overrides the open control to close the switch. Also, excessive current will cause switching on the fpf2500, fpf2501, fpf2503 and fpf2505. The fpf2500, fpf2503 and fpf2505 have an auto-restart feature that automatically turns the switch on after 640ms. For the FPF2501, the ON pin must be toggled to turn on and toggled again. The fpf2502, fpf2504 and fpf2506 do not shut down in overcurrent conditions, but remain active in constant current mode operation and thermal shutdown or undervoltage lockout deactivated as long as they are on. Current Limit The current limit ensures that the current through the switch does not exceed the maximum value, but is not limited to less than the minimum value.

For the fpf2500, fpf2501 and fpf2502, the current limited by the part can be selected by an external resistor connected to ISET. Methods for selecting resistors can be found in the Application Information section of the Information Office. For FPF2503 and FPF2504, the minimum current is 400mA and the maximum current is 800mA, for the fpf2505-fpf2506 the minimum current is 800mA, and the maximum current is 1600mA. The fpf2500, fpf2501, fpf2503 and FPF2505 typically have a 5ms blanking time during which the switch will act as a constant current source. At the end of the blanking time, the switch closes. For the FPF2503 and FPF2505, at the end of the blanking time, after the switch will close, the flagb pin will activate to indicate that current limit has occurred. The fpf2502, fpf2504 and FPF2506 do not have a current limit blanking period, so they will remain in a constant current state. For fpf2504 and fpf2506, the current constraint flag B is activated immediately. The fpf2502, fpf2504, and fpf2506 devices will remain in a constant current state until the on-pin cycle or thermal shutdown turns off the switch. Undervoltage lockout if the input voltage falls below the undervoltage lockout threshold. With the ON pin activated, the input voltage rising above the undervoltage lockout threshold will cause the switch to limit current overshoot. Thermal Shutdown Thermal shutdown protects the mold from excessively high temperatures generated internally or externally. In an overtemperature condition, the switch is closed. The switch automatically turns on again if the mold temperature drops below the critical temperature

The output capacitor should be at vout and ground. This capacitor prevents parasitic plate inductance from driving the output voltage below ground when the switch is open. For the fpf2501, fpf2503 and fpf2505, the total output capacitance needs to be kept below the maximum value cout(max) to prevent the part from turning off the switch from recording the overcurrent condition to turning. The maximum output capacitance can be determined by the following formula, Power Dissipation Due to the wide range of input voltages that the part can accept and the high current for which the current limit can be set, care must be taken to prevent excessive power dissipation of the part from switching off the supply to the load. Normally operating as a switch, the power dissipated in this part will depend on the set level of the current limit. For a typical load of 0.5A, the dissipated power is typically beyond the normal thermal capacity of the package, but thermal shutdown inside the part will prevent damage to the shutdown switch once the maximum junction temperature has been reached. If the part goes into current limit when the output is shorted to ground. For fpf2500, fpf2503 and fpf2505 power consumption increases with auto restart time, trestart and overcurrent blanking time tblank so that the maximum power consumed is, Board Layout For best performance, all traces should be as short as possible. To be most effective, input and output capacitors should be placed close to the device to minimize the effects of parasitics during normal and short-circuit operation that may have slight inductance. Using wide traces for VIN (vin), VIN (vout), and ground (gnd) will help minimize parasitic electrical effects while minimizing enclosure-to-ambient thermal impedance